Lack of chinook salmon to eat stresses Puget Sound's endangered killer whales more than boat noise, researchers have learned.

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Lack of food — not noise from whale-watching boats — is most stressful to Puget Sound’s endangered killer whales, researchers have learned.

Levels of certain stress hormones decreased in samples of orca scat gathered during the time of highest vessel traffic, instead of increasing, researchers found. They surmise this is because at the same time, the whales’ favorite food, chinook salmon, was most abundant.

Interestingly, the orcas’ stress-hormone levels only increased when vessel noise was higher if there also were lower levels of food available at that time.

“I like to call it my buffet-in-a-bar example,” said Katherine Ayres, lead author of a paper on the study published in PLoS ONE, released Wednesday. Patrons in a noisy bar won’t mind the racket if all their favorite foods are piled high on the buffet. “But you go there and they are only serving rice and potatoes, and it’s super noisy and crowded, then it’s, ‘I am not getting a good meal and these boats are driving me crazy.’ “

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Sam Wasser, director of University of Washington’s Department of Biology Center for Conservation Biology, said the study points to the importance of putting fish first as managers look for the priority management steps, amid reducing toxins and pollution, vessel noise and improving food supply, for orca recovery.

“If you are a manager, you really want to know what are the relative importance of those, and how do they interact, and our study did that; it found that fish are the most important,” Wasser said.

Efforts to build up Puget Sound chinook have been under way since before they were listed as threatened more than 10 years ago.

Yet despite the knowledge that habitat is key to chinook survival, a review of the implementation of the recovery plan for chinook for NOAA Fisheries last year showed the region has continued to lose habitat since the listing.

From 2001 to 2006, the amount of developed land in Puget Sound increased about 3 percent, with nearly two-thirds of that converted from forests or agricultural land to pavement. That translates to a loss of about 10,700 more acres of forest cover and 4,300 acres of agricultural land over that period.

Western Washington Treaty Tribes reported in a 2011 White Paper that salmon returns have continued to dwindle to the point that tribes are catching fewer salmon today than before the 1974 Boldt decision, which secured their right to half the salmon catch.

To some it’s no surprise that food supply and habitat that will support healthy salmon runs would be seen as key to orca recovery. Ken Balcomb of the Center for Whale Research said he remembered seeing far more orcas back when he also used to see far more fishing boats off the west coast of the San Juan Islands. The whales never seemed to mind the boats — back when there were lots of fish.

“This is what I have been saying all along,” Balcomb said.

Lynda V. Mapes: 206-464-2736 or

On Twitter @lyndavmapes.

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